When a substance such as human tissue is subjected to a uniform magnetic field (polarizing field Bo), the individual magnetic moments of the spins in the tissue attempt to align with this polarizing field, but process about it in random order at their characteristic Larmor frequency. If the substance, or tissue, is subjected to a magnetic field (excitation field B.sub.1) which is the x-y plane and which is near the Larmor frequency, the net aligned moment, Mz, may be rotated, or "tipped", into the x-y plane to produce a net transverse magnetic moment M. A signal is emitted by the excited spins after the excitation signal B.sub.1 is terminated and this signal may be received and processed to form an image.
When utilizing these signals to produce images, magnetic field gradients (G.sub.x, G.sub.y and G.sub.z) are employed. Typically, the region to be imaged is scanned by a sequence of measurement cycles in which these gradients vary according to the particular localization method being used. The resulting set of received NMR signals are digitized and processed to reconstruct the image using one of many well known reconstruction techniques.
When attempting to define the volume of coverage for an MRI scan, the NMR system operator may desire to prescribe a specific two dimension scan plane within the total volume of coverage. This process can be particularly useful when prescribing a double oblique, off axis two dimensional scan plane of complex anatomy such as vasculature.
Typically, an operator must first acquire an axial, sagittal or coronal "scout" image of the structure of interest. Such scout image is then displayed and the operator uses such scout image to graphically prescribe the 2D section or 3D imaging volume. Three-plane localizer acquisitions have been developed which quickly acquire standard orthogonal scout images and then display such images with graphic prescription overlay tools. Such procedure allows the operator to rapidly prescribe subsequent acquisition imaging volumes of the structure of interest. FIG. 3 depicts the prior art which uses scout images and prescribe process using those orthogonal planes.
Following data acquisition the MR system reformats the previously acquired volume data set. Such reformatting is accomplished by pixel data post-processing. Such reformatted volume data set is used to display a particular projection or image plane, a reference image or a set of orthogonal reference images as determined by the operator. Such image is usually displayed with an intersection reference line. The intersection reference line is updated to reflect the position of the projection or visualization plane of the image of the structure of interest. FIG. 4 depicts the prior art process of such reformat and intersection reference line display which is performed following data acquisition.